Conventionally various kinds of high-temperature heat-resistant alloys such as a Ni-base alloy, a Co-base alloy and an Ir-base alloy have been known as a constituent material of a high-temperature member such as a jet engine and a gas turbine, or a tool for friction-stirring welding (FSW) and the like. For example, as a new substitute heat-resistant alloy for the Ni-base alloy, there has been disclosed an Ir—Al—W-base alloy of the Ir-base alloy (Patent Literature 1).
The present applicant has developed, as a heat-resistant alloy having novel composition, a heat-resistant alloy which is based on a Ni—Ir—Al—W-base alloy. This NiIr-base heat-resistant alloy is an alloy having essential additive elements of Ir, Al, and W added to Ni, including Ir: 5.0 to 50.0 mass %, Al: 1.0 to 8.0 mass %, W: 5.0 to 20.0 mass %, and a balance being Ni.
The aforementioned novel NiIr-base heat-resistant alloy utilises a precipitation strengthening action of a γ′ phase ((Ni, Ir)3(Al, W)) which is an intermetallic compound having an L12 structure as a strengthening mechanism. Since the γ′ phase exhibits reverse temperature dependence such that strength increases with rising in temperature, the γ′ phase can impart excellent high-temperature strength and high-temperature creep properties to the alloy. Though the use of the strengthening action of the γ′ phase is similar to the strengthening mechanism in the conventional Ni-base heat-resistant alloy, the NiIr-base heat-resistant alloy by the applicants is improved in the phenomenon of the γ′ phase under high temperature, and has a better high-temperature stability than the Ni-base heat-resistant alloy.
Incidentally, for a production of an alloy, in general, the production includes steps for producing an alloy ingot of desired composition by a melting and casting method as a main step, and optional additional processing and heat treatment steps to produce an alloy product. The NiIr-base heat-resistant alloy by the applicant can be produced by the general melting and casting method, and further an aging heat treatment is conducted for precipitating the γ′ phase which is the main strengthening mechanism. The aging heat treatment may preferably be conducted by heating at a temperature in the temperature range of 700 to 1300° C. for 0.5 minutes to 72 hours.